You can spend A LOT. It really depends on how much you want to spend and how big of a throat you want.
You can also save a lot if you go the used route - that is what I did with my Bailey. Check your Craigslist or join some of the yahoogroups.
I will say that Nolting puts their prices out in the open
http://nolting.com/catalog.php
Note - Noting just acquired Hinterberg so if you were looking to go with a Voyager type of model, you call them now ;)
So does Gammill
http://gammill.com/index.php?m=longarm_models
And Bailey...
http://www.baileyssewingcenter.com/
(that is what I have sitting in my craft room, unused. I've been kind of scared of it. I will be plunging in soon though)
You will probably also get cheaper prices if you deal directly through the dealers.
The prices are generally out there - for the sticker price. What you end up with if you go through a dealer or get a used set up is different.